Optical system active alignment process including alignment structure attach, position search, and deformation

ABSTRACT

Mounting and alignment structures for optical components allow optical components to be connected to an optical bench and then subsequently aligned, i.e., either passively or actively, in a manufacturing or subsequent calibration or recalibration, alignment or realignment processes. The structures comprise quasi-extrusion portions. This portion is “quasi-extrusion” in the sense that it has a substantially constant cross section in a z-axis direction as would be yielded in an extrusion manufacturing process. The structures further comprise at least one base, having a laterally-extending base surface, and an optical component interface. At least one armature connects the optical component interface with the base. In the preferred embodiment, the base surface is securable to an optical bench.

RELATED APPLICATIONS

This application claims the benefit of the filing date of U.S.Provisional Application No. 60/165,431, filed Nov. 15, 1999, which isincorporated herein by this reference in its entirety.

This application also claims the benefit of the filing date of U.S.Provisional Application No. 60/186,925, filed Mar. 3, 2000, which isincorporated herein by this reference in its entirety.

BACKGROUND OF THE INVENTION

Component alignment is of critical importance in semiconductor and/orMEMS (micro electro-mechanical systems) based optical systemmanufacturing. The basic nature of light requires that light generating,transmitting, and modifying components must be positioned accuratelywith respect to one another, especially in the context offree-space-optical systems, in order to function properly andeffectively in electro-optical or all optical systems. Scalescharacteristic of semiconductor and MEMS necessitate sub-micronalignment accuracy.

Consider the specific example of coupling a semiconductor diode laser,such as a pump laser, to a fiber core of a single mode fiber. Only thepower that is coupled into the fiber core is usable to optically pump asubsequent gain fiber, such as a rare-earth doped fiber or regularfiber, in a Raman pumping scheme. The coupling efficiency is highlydependent on accurate alignment between the laser output facet and thecore; inaccurate alignment can result in partial or complete loss ofsignal transmission through the optical system.

Moreover, such optical systems require mechanically robust mounting andalignment configurations. During manufacturing, the systems are exposedto wide temperature ranges and purchaser specifications can explicitlyrequire temperature cycle testing. After delivery, the systems can befurther exposed to long-term temperature cycling and mechanical shock.

Solder joining and laser welding are two common mounting techniques.Solder attachment of optical elements can be accomplished by performingalignment with a molten solder joint between the element to be alignedand the platform or substrate to which it is being attached. The solderis then solidified to “lock-in” the alignment. In some cases, anintentional offset is added to the alignment position prior to soldersolidification to compensate for subsequent alignment shifts due tosolidification shrinkage of the solder. In the case of laser welding,the fiber, for example, is held in a clip that is then aligned to thesemiconductor laser and welded in place. The fiber may then also befurther welded to the clip to yield alignment along other axes.Secondary welds are often employed to compensate for alignment shiftsdue to the weld itself, but as with solder systems, absolutecompensation is not possible.

Further, there are two general classes of alignment strategies: activeand passive. Typically in passive alignment of the optical components,registration or alignment features are fabricated directly on thecomponents or component carriers as well as on the platform to which thecomponents are to be mounted. The components are then mounted and bondeddirectly to the platform using the alignment features. In activealignment, an optical signal is transmitted through the components anddetected. The alignment is performed based on the transmissioncharacteristics to enable the highest possible performance level for thesystem.

SUMMARY OF THE INVENTION

The problem with conventional alignment processes is that they requirevery specialized machines to implement. Even then, the alignment processis typically slow.

It has been suggested to utilize plastic deformation of opticalcomponent structures during alignment processes. The problem, however,with these proposed systems, it that they only provided limited range ofmotion during the alignment process, which, even under optimalconditions, resulted in sub-optimal alignment.

In general, according to one aspect, the invention features an opticalsystem active alignment process. It comprises activating an optical linkin the optical system and detecting an optical signal after transmissionthrough the optical link. An optical component is positioned on adeformable structure relative to the active optical link by moving theoptical component in a plane that is orthogonal to a propagationdirection of the optical signal at the optical component. Thispositioning is performed, while maintaining a position of the opticalcomponent along an axis that is parallel to the propagation direction ofthe optical signal. The structure is plastically deformed to align theoptical component relative to the optical link.

The advantage of this positioning system surrounds the fact thatconventional robot/pick-and-place machines can be used to locate thedeformable structure positioning the optical component with relativelyhigh precision relative to other optical components, especially alongthe length of the optical path. It is difficult, however, to locate theoptical component in a plane that is orthogonal to this optical path,however. This is because there are inaccuracies in how the opticalcomponent is positioned on the structure. Moreover, the exact locationof the optical signal's path may not be known with great accuracy,either in its height above an optical bench and/or laterally. Theability of the deformable structure to enable optical componentpositioning in a plane that is orthogonal to the optical signalpropagation direction allows the proper alignment of the opticalcomponent to be achieved during active alignment. This alignment isperformed while minimizing any degradation in alignment in a path thatis parallel to the optical signal's path.

The above and other features of the invention including various noveldetails of construction and combinations of parts, and other advantages,will now be more particularly described with reference to theaccompanying drawings and pointed out in the claims. It will beunderstood that the particular method and device embodying the inventionare shown by way of illustration and not as a limitation of theinvention. The principles and features of this invention may be employedin various and numerous embodiments without departing from the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, reference characters refer to the sameparts throughout the different views. The drawings are not necessarilyto scale; emphasis has instead been placed upon illustrating theprinciples of the invention. Of the drawings:

FIG. 1 is a perspective view of a first embodiment of a mounting andalignment structure according to the present invention;

FIG. 2 is a front plan view of the first embodiment mounting andalignment structure;

FIG. 3A is a perspective view showing a second embodiment of themounting and alignment structure according to the present invention;

FIG. 3B is a front plan view showing the dimensions of the secondembodiment structure;

FIG. 4 is a perspective view showing a third embodiment of the mountingand alignment structure according to the present invention;

FIG. 5A is front plan view showing fourth embodiment of the inventivemounting and alignment structures;

FIG. 5B is perspective view showing a related embodiment of theinventive mounting and alignment structures;

FIG. 6 is front plan view showing fifth embodiment of the inventivemounting and alignment structures;

FIG. 7 is a front plan view of a sixth embodiment of the mounting andalignment structures accounting to the present invention;

FIG. 8 is a front plan view of a seventh embodiment of the inventivemounting and alignment structures;

FIGS. 9 and 10 show eighth and ninth embodiments of the inventivemounting and alignment structures;

FIG. 11 is a front plan view of a tenth embodiment of the inventivemounting and alignment structures in which separate structures areintegrated onto a single base according to the invention;

FIG. 12 is a plan view showing an eleventh embodiment of a mounting andalignment structure according to the present invention;

FIG. 13 is a plan view showing twelfth embodiment of the presentinvention;

FIG. 14 is a plan view showing a thirteenth embodiment of an inventivemounting and alignment structure for passive component alignment;

FIGS. 15A and 15B are front plan views showing the fourteenth embodimentof the mounting and alignment structure and it deployment for mounting asecond optical component in proximity to another optical component;

FIGS. 16A, 16B, 16C are cross-sectional views of the plating andlithography processes used to fabricate the mounting and alignmentstructures according to the invention;

FIGS. 17A-17F illustrate a process for manufacturing mounting andalignment structures that have non-constant cross-sections along az-axis for portions of structures;

FIGS. 18A and 18B are a perspective diagram illustrating the processsteps associated with installing optical components on the mounting andalignment structures and mounting and alignment structures on theoptical bench;

FIG. 19 is a perspective drawing of a laser optical signal source thatcouples a beam into an optical fiber held by a mounting and alignmentstructure, according to the present invention;

FIG. 20 is a process diagram illustrating the optical system activealignment process according to the present invention;

FIG. 21 is a perspective top view showing the jaws of an alignerengaging the handle of a mounting and alignment structure to deform thestructure during an alignment process;

FIG. 22 is a plot of force and optical response on the vertical axis asa function of displacement or strain on the horizontal axis illustratingthe inventive alignment process;

FIG. 23 is the plot of force along the y-axis as a function ofdisplacement illustrating constraints in the selection of the yieldforce;

FIG. 24 is a perspective view showing a fifteenth, composite structureembodiment of the invention;

FIG. 25 is a schematic perspective view of a sixteenth, dual materialembodiment of the invention;

FIG. 26 is a schematic diagram illustrating a production line foroptical systems, according to the present invention; and

FIGS. 27A, 27B, and 27C are partial plan views of the mounting andalignment structures showing three different configurations for thealignment channels.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Mounting and alignmentstructure configuration

FIG. 1 shows an exemplary mounting and alignment structure, which hasbeen constructed according to the principles of the present invention.

Generally, the alignment structure 100 comprises a base 110, an opticalcomponent interface 112, and left and right armatures 114A, 114B, whicheither directly connect, or indirectly connect, the base 110 to theinterface 112.

The base 110 comprises a laterally-extending base surface 116. In theillustrated example, the base surface 116 extends in a plane of the xand z axes, generally.

The base/base-surface comprise alignment features. In some embodiment,these features are adapted to mate with preferably opposite-genderedalignment features of an optical bench. In the specific illustratedimplementation, the alignment features are used by machine vision tomatch to alignment marks or features of a bench. Specifically, thealignment features comprise a wide, U-shaped cut out region 120. Threefemale alignment channels 118 are further provided that extend along theentire depth of the structure in the direction of the z-axis. TheU-shaped cut-out region 120 has the added advantage of minimizing thecontact area and thus stress in the interface between the structure andthe bench or other surface to which it is attached.

In the illustrated implementation, each of the armatures 114A, 114Bcomprises two segments 122 and 124. Specifically, and for example,armature 114B comprises two segments, 122B and 124B.

The vertically-extending segments 122A, 122B, i.e., extending at leastpartially in the y-axis direction, have two flexures 126A, 126B alongtheir length, in the illustrated embodiment. These flexures are regionsof reduced cross-sectional area in the segments, which regions extend inthe direction of the z-axis. The vertically-extending segments 122facilitate the positioning of an optical component, installed on theinterface 112, along the x-axis; the flexures 126A, 126B facilitate thepivoting of the segments 122A, 122B in a plane of the x and y axes. Apurpose of the flexures is to isolate regions of microstructural change,such as occurring in plastic deformation, in order to make the yieldforces, for example, readily predictable. Also, the flexures localizedeformation on the armatures and consequently decrease the amount offorce/movement required in the optical component before plasticdeformation is initiated in the armature.

Horizontally-extending (i.e., extending in the direction of the x-axis)segments 124A, 124B each comprise, in the illustrated embodiment, twoflexures 128A, 128B. These flexures are also regions of reducedcross-sectional area in the respective segments, the flexures extendingin the direction of the z-axis.

The horizontally-extending segments 124A, 124B allow the positioning ofan optical component, installed on the optical component interface 112,generally vertically along the y-axis. Armature deformation isfacilitated by respective flexures 128A, 128B.

In one implementation, the optical component is bonded to the opticalcomponent interface 112, and specifically bonding surface 132. Thisbonding is accomplished either through polymeric adhesive bonding orpreferably solder bonding. In other implementations, thermocompressionbonding, laser welding, reactive bonding or other bonding method areused.

In the illustrated embodiment, the component interface further includesstructure-component alignment features 113. In the illustratedembodiment, the structure-component alignment features comprise slotsextending in the z-axis direction from the component bonding surface132. As a result, corresponding male-projections of an optical componentengage the slots 113 to locate and align the optical component over theoptical port 134 both along the x-axis and y-axis.

The optical component interface, in some implementations, comprises aport 134 for enabling an optical signal to pass transversely through thestructure. This enables optical access to the optical component byeither facilitating the propagation of an optical signal to and/or awayfrom the component.

To facilitate the grasping and placement of the structure 100, a handle136 is also preferably provided on the structure. In the illustratedembodiment, the handle 136 comprises two V- or U-shaped cut out regionson either side, near the top of the top of the structure. In theillustrated example, they are integral with the optical componentinterface 112.

The handle 136 enables the manipulation of the structure 100 whenattached to the bench 10. Specifically, the right cut-out is engaged todisplace the structure to the left, for example. To displace thestructure vertically or in the y-axis direction, both cut-outs areengaged enabling the structure to be pressed down toward the bench 10 orpulled away from the bench.

To further facilitate grasping and installation on the bench, wingportions 121A, 121B are provided on each armature. These are used by aheated vacuum chuck to enable manipulation of the structure andsubsequent heating for solder bonding. The short distance between thewings 121 and the base surface 116 facilitate good heat transfer.

FIG. 2 is a front plan view of the first embodiment of the mounting andalignment structure 100, illustrated in FIG. 1. This view illustratesthe construction of the left and right armatures 114A, 114B, andspecifically how the armatures are constructed from respectivehorizontally-extending segments 124 and vertically extending segments122.

Also shown is the extent of the bonding surface 132. Typically, a soldermaterial is first applied to the surface 132. Later, the opticalcomponents and/or structures are heated and brought into contact witheach other to effect the solder bonding. In other embodiments, epoxybonding processes are used in which epoxy is first applied to thesurface 132.

FIG. 3A shows a second embodiment of the mounting and alignmentstructure. This embodiment shares a number of similarities with thefirst embodiment illustrated in FIGS. 1 and 2. Specifically, themounting surface 116 has slot-like alignment channels 118 for visualalignment.

Turning to the armatures 114A, 114B, vertically-extending portions 122A,122B are provided similar to the first embodiment. Two horizontallyextending portions 154, 155, however, are provided on each armature oneach side of the mounting and alignment structure 100. Specifically, thearmature 114B comprises two horizontally extending segments 154B, 155B,which extend generally from the vertically extending portion 122B to theoptical component interface 112. Specifically, a linkage portion 158Bconnects the distal ends both of the horizontally-extending portions154B, 155B to the vertically-extending portion 122B of armature 114B.

The second embodiment of FIG. 3A illustrates a further configuration forthe optical component interface 112. Specifically, the optical interface112 of the second embodiment comprises a V or U-shaped cut-out region orslot 152 extending through the mounting and alignment structure 100 inthe direction of the z-axis. This open-slot configuration allows afiber, schematically illustrated as F to be installed vertically in thedirection of arrow 159 down into the slot 152. In the typicalimplementation, the fiber F is then bonded to the surface 132 in thebottom of the slot. Solder bonding is preferably used, but otheralternatives such as epoxy bonding exist.

In the preferred embodiment, the depth of the slot relative to thelocations of the attachment points of the armatures is designed toresist any rocking in response to z-axis forces exerted on the structureby the fiber. Specifically, some movement in response to z-axis forcesis unavoidable. Slot depth is controlled, however, so that the fiberaxis does not move in response to these forces.

In alternative embodiments, the handles 136 are engaged and the U-shapedslot crimped closed by applying force along arrow 157 to secure theoptical component, such as fiber.

FIG. 3B shows exemplary dimensions of the third embodiment.Specifically, the height h of the illustrated embodiment is 1.1millimeters (mm). Generally the structures typically have height ofgreater than 0.5 mm to promote manipulation. To provide adequateclearance in standard packages, the structures are typically less then2.0 mm in height. The width w of the illustrated structure is 1.9 mm.Here again, the width is preferably greater than 0.5 mm to facilitatestable installation on the bench. To provide acceptable componentpacking densities and clearance between components the width w oftypically less than 4 mm is desirable.

FIG. 4 shows a third embodiment mounting and alignment structure 100that shares many similarities with the structures described inconnection with FIGS. 1-3. It has a base 110 and laterally-extendingbase surface 116. Further, the third illustrated embodiment has anoptical component interface 112 with an optical port 152. In thisexample, the handle 136 is more pronounced, extending vertically upwardfrom the interface 112.

V-shaped alignment features 210 are provided on the base surface forengaging complementary V-shaped alignment trenches in the bench.

One of the more distinguishing characteristics is the armatures 114A and114B. Instead of having segments that extend parallel to the x and yaxes, each armature comprises two diagonally extending segments 212, 214that intersect substantially at a right angle with respect to eachother. Further, the armatures have no discrete flexure system butinstead have a relatively constant cross-section along the length of thearmatures.

Further, the optical component interface 112 comprises a relativelyclosed slot-shaped optical component mounting slot 152. In oneembodiment, a fiber is inserted into the slot 152 and then the slot iscrimped closed to secure the fiber therein. Further, a handle 136 isprovided extending vertically from the optical component interface 112.In the illustrated example, the handle 136 has right and left extensionson either side of the slot 152.

Another distinction relative to the third embodiment of FIG. 4 is theuse of a z-axis flexure. Specifically, the base 110 comprises a frontplate portion 422 and a rear plate portion (not shown). Thus, the base110 is a hollow box-configuration. The use of the Z-axis armature allowscontrolled flexing when stress is exerted in a rotational manner aroundthe x-axis or θ direction.

FIG. 5A shows an embodiment in which the base is divided into twoseparate base portions 110A, 110B to promote a stable structure-benchinterface while simultaneously minimizing the contact area subject tothermal expansion mismatch stresses. In order to make the device morerobust during manufacturing of the structure and during its installationon the optical bench, a spring-like connecting element 310 connects thetwo halves of the base 110A, 110B. This element is clipped prior toinstallation or intentionally collapsed.

FIG. 5B shows a related embodiment with similar reference numeralsindicating similar parts. This embodiment is notable in that the anglebetween vertically-extending segments 126 and the horizontally-extendingsegments 124 form an obtuse angle. In some applications thisconfiguration facilitates alignment.

FIG. 6 shows a fifth embodiment, being closely related to the fourthembodiment of FIG. 5A. Here, the optical component interface comprisestwo separate, divided portions 112A, 112B. In this embodiment, anoptical component, such as an optical fiber f is inserted into thevolumetric region between the two halves 112A, 112B of the interface.The two halves 112A, 112B are snapped closed around the fiber F.

FIG. 7 shows a sixth embodiment of a mounting and alignment structure.This embodiment is notable relative to the previously discussedembodiments in that the armatures 114A, 114B have continuous flexuresdistributed across the length of the armatures. The flexures are notlocated at specific flexure points as illustrated in some of theprevious embodiments. In this embodiment, the armatures act asdistributed flexing components that are subject to plastic deformation.

FIG. 8 shows a seventh embodiment of the mounting and alignmentstructures. This embodiment is notable in that the armatures 114A, 114Bare relatively rigid such that they will resist any flexing or plasticdeformation. Specifically, the armatures 114A, 114B have no discreteflexures as discussed relative to FIG. 1 nor do they have a continuousflexure system as illustrated in FIG. 7 as illustrated by the fact thatthe armatures are relatively thick. As a result, the embodiment of FIG.8 is typically used mostly for mounting fibers that pass outside of themodule or package through a fiber feed-through. The seventh embodimentresists strain to any stress exerted on, for example, a fiber F held inthe interface 112.

Typically, the seventh embodiment is used in conjunction with a secondmounting and alignment structure. The first mounting and alignmentstructure is proximate to the end of the fiber and enables alignment ofthe fiber end in the x, y plane. The seventh embodiment alignmentstructure is used to minimize the stress transmitted through the fiberto the structure used for fiber-end alignment.

FIG. 9 illustrates an eighth embodiment with continuous flexurearmatures 114A, 114B and an optical interface 112 that would beappropriate for an optical component other than an optical fiber.Specifically, a mirror or lens is mounted on the optical interface 112by bonding such as solder or epoxy bonding. The port 134 enables opticalaccess to that component in which an optical signal is reflected by theoptical component or passes through the component thus also passingthrough the port 134.

FIG. 10 shows ninth embodiment where the base 110 is a relatively wideone-piece base.

FIG. 11 shows another embodiment in which four structures 100A-100D areintegrated on a common base 110. This system is useful for holdingoptical components, such as optical fibers for four physically paralleloptical channels or paths. According to the invention, each opticalfiber is separately aligned with separate alignment characteristics ofthe structures. The common base, however, enables multiple, simultaneouspassive alignment of the structures/fibers in a single pick andplacement step.

FIG. 12 shows a non-laterally symmetric mounting and alignment structureaccording to an eleventh embodiment. It comprises a base 110 and anarmature 114 extending from the base vertically. The armature comprisesa vertical segment 122 and a horizontally extending segment 124. Thehorizontally extending segment 124 terminates in a component interface112. A handle 136 extends vertically from this interface.

FIG. 13 shows a non-laterally symmetric mounting and alignment structureaccording to a twelfth embodiment of the present invention. In thiscase, the base 110 extends in a vertical, y-axis direction such that itmay be attached onto a side-wall of a module or another mounting andalignment structure. It further has an horizontally extending armature114 and a component interface 112 adapted to hold a fiber concentricallyin the center or abut against a fiber to improve its alignment.

FIG. 14 is a plan view of a mounting structure for exclusively passivemounting of an optical component. Specifically, the thirteenthembodiment has a base 112 and an integral optical component interface112. It further has a port 134 for enabling access to the opticalcomponent. This embodiment does not have armatures and consequently isonly susceptible to small alignment shifts. It is used mostly to holdcomponents when their horizontal or vertical positioning isnon-critical, such as, for example, a filter mirror in some systemdesigns.

FIG. 15A shows a mounting and alignment structure for mountingrelatively large MEMS filter device, in a current implementation.

Specifically, the fourteenth embodiment mounting and alignment structurehas a divided base 110A, 110B. From each base, respective armatures114A, 114B extend. The armatures each comprise a vertically extendingportion 122A, 122B and a horizontally extending portion 124A, 124B. Theoptical component interface 112 is relatively large and is designed tohold an optical component mounted to the mounting surface 132, forexample. The handle 136 is integral with the interface in thisembodiment.

FIG. 15B illustrates the deployment of the fourteenth embodimentalignment structure 100B with one of the previously discussed alignmentstructures 100A. In typical installation and alignment, the mounting andalignment structure 100A is first installed on an optical bench 10.Alignment structure is then preferably deformed, in an active alignmentprocess, for example, such that the optical component is properlylocated relative to the optical path. Subsequently, after the alignmentof the optical component held by mounting and alignment structure 100A,the mounting structure 100B is installed with its own optical component.Then, this second alignment structure 100B is then tuned, in an activealignment process, for example, so that the second optical component isproperly located in the optical path. The relative size differencesbetween alignment structure 100A and 100B allows series alignments oftheir respective optical components even though the optical componentsare mounted in close proximity to each other on the bench 10.

Mounting Structure Manufacturing

FIGS. 16A-16C are cross-sectional views of the mounting and alignmentstructures 100 during the manufacturing process.

Specifically, as illustrated in FIG. 16A, a thick PMMA resist layer 414is bonded to a seed/release layer 412 on a substrate 410.

The depth d of the PMMA layer 414 determines the maximum thickness ofthe subsequently manufactured quasi-extrusion portion of the mountingand alignment structure. As a result, the depth determines the rigidityof the mounting and alignment structure 100 to forces along the Z-axis.In the preferred embodiment, the depth and consequently Z-axis thicknessof the mounting and alignment structures is in the range of 500-1000microns. Thicker structures are typically used for strain relief-typestructures. According to present processes, the structures, andconsequently the depth of the PMMA layer is as deep as 2000 microns toproduce structures of same thickness.

FIG. 16B illustrates the next fabrication step in the mounting andalignment structure 100. Specifically, the thick PMMA resist layer ispatterned by exposure to collimated x-rays. Specifically, a mask 416,which is either be a positive or negative mask having the desiredpattern for the structure, is placed between the x-ray source such as asynchrotron and the PMMA layer 414. The PMMA layer 414 is then developedinto the patterned layer 414A as illustrated in FIG. 16B.

FIG. 16C shows the formation of the quasi-extrusion portion of themounting structure 100. Specifically, in the preferred embodiment, thequasi-extrusion portion is formed via electroplating. The preferredplating metal is nickel according to the present embodiment. Nickelalloys, such as a nickel-iron alloy, are used in alternativeembodiments. Alternatively gold or a gold alloy is used in still otherembodiments. Currently, alternative metal and alloys include: silver,silver alloy, nickel copper, nickel cobalt, gold cobalt and alloys ladenwith colloidal oxide particles to pin the microstructures.

FIGS. 17A-17F illustrate a process of manufacturing the z-axis flexure422 previously discussed with reference to FIG. 4. Specifically, asillustrated in FIG. 17A, after the formation of the quasi-extrudedportion of the mounting and alignment structure, the substrate 410 isremoved from the seed layer 412. Thereafter, an additional photoresist420 layer is coated and then patterned as illustrated in FIG. 17B forone plate of the z-axis flexure. Thereafter, a further electroplatingstep is performed to fabricate the plate of the z-axis flexure 422 ontothe existing cross-sectionally constant section 100.

In FIG. 17D, a second photoresist is formed and then patterned on thereverse side of the structure 100 and first PMMA layer 414. The etchingis performed through the seed layer 412. Another plating step isperformed and the second plate of the z-axis flexure 428 is manufacturedas illustrated in FIG. 17E. Thereafter, as illustrated in FIG. 17F, theremaining photoresist layer 424, seed layer 412, and PMMA layer 414 areremoved leaving the hollow box-shaped structure illustrated. This boxshaped structure forms the bottom base section 422 of the mounting andalignment structure illustrated in FIG. 4.

Mounting Structure-optical Component Bench Installation

FIG. 18A illustrates the process associated with installing opticalcomponents on the optical bench 10.

The bench is preferably constructed from mechanically robust, chemicallystable, and temperature stable material, such as silicon, berylliumoxide, aluminum nitride, aluminum silicon carbide, beryllium copper. Itis typically metal or ceramic coated with gold or a gold alloy forexample.

Specifically, in a step 450, optical component 20 is installed on afirst mounting and alignment structure 100-1. Specifically, the opticalcomponent 20 is preferably bonded to the mounting and alignmentstructure 100-1. In the preferred embodiment, a solder bonding is usedin which solder is first applied to a periphery of the optical componentand/or the bonding surface 132 of the optical component interface 112.Then the optical component is brought into contact with the mountsurface 132 of the structure's component interface 112. The solder isthen melted and allowed to solidify.

Also in the preferred embodiment, complimentary alignment features inthe optical component 20 and the interface 112 facilitate alignment andproper seating between the component 20 and structure 100-1.Specifically, in alignment channels 113 (see FIGS. 1 and 2) are formedon the structure's interface. Marks or projections 451 on the opticalcomponent 20 engage the slots 113 to ensure reproducible installation ofthe component 20 on the structure 100-1.

In other embodiments, the component 20 is epoxy bonded or bonded usinganother adhesive bonding technique to the structure.

Then, in a structure-bench mounting step 452, the structure 100-1 isbrought into contact with the optical bench 10 and bonded to the bench.In the preferred embodiment, solder bonding is used in which the benchis held in a heated chuck of a pick-and-place machine while thepreheated structure is brought into contact with the bench. The heat isthen removed to solidify the solder.

As illustrated in connection with alignment structure 100-2, for otheroptical components, the mounting steps are reversed. In this example,the mounting and alignment structure 100-2 is contacted and bonded tothe bench in a structure-bench bonding step 454. Thereafter, the opticalfiber F is seated in the U-shaped port 152 in step 457 of the mountingand alignment structure 100-2. Thereafter, the fiber is either bonded tothe interface bonding surface 132 or the U-shaped slot is crimped suchthat the fiber is secured in the bottom of the U-shaped port. Thus, thefiber endface EF is secured to the optical bench in proximity to theoptical component, such as thin film filter or mirror 20, held bystructure 100-1.

FIG. 18B also illustrates the process associated with installingMEMS-type optical components on the optical bench 10. Specifically, inthis embodiment, a front mirror 470 is first bonded over a reflectivemembrane of the MEMS device 472 in a first bonding step 474. Then, theMEMS device 472 is bonded to the alignment structure 100 in a secondbonding step 476. Then in a bench-bonding step 478, the compositeMEMS/structure is bonded to the bench 10.

Mounting Structure Deformation in Alignment

FIG. 19 is a perspective view of a fiber optic laser optical signalsource system, which has been constructed according to the principles ofthe present invention. Specifically, the laser source system 610comprises a laser chip 612, which has been mounted on a hybrid substrate614. Typically, this substrate supports the electrical connections tothe chip 612 and possibly also comprises a thermoelectric cooler formaintaining an operating temperature of the chip 612. The hybridsubstrate 614 is in turn installed on an optical bench portion 10 of apackage substrate 622. A detector 616 is located behind the chip 612 onthe bench 10 to detect rear facet light and thereby monitor theoperation of the laser 612.

Light emitted from a front facet 618 of the chip 612 is collected by afiber f for transmission outside the optical system 610. In oneimplementation, the light propagating in fiber f is used to opticallypump a gain fiber, such as a rare-earth doped fiber or regular fiber ina Raman pumping scheme. In other implementations, the laser chip 612 ismodulated in response to an information signal such that the fibertransmits an optical information signal to a remote detector. In stillother implementations, the laser chip 612 is operated to run in a CWmode with modulation performed by a separate modulator such as aMach-Zehnder interferometer.

An optical component mounting and alignment structure 100, according tothe invention, is installed on the optical bench portion 10 of thepackage substrate 622. As discussed previously, the optical bench hasalignment features 620, which mate with opposite-gender alignmentfeatures on the base surface of the mounting and alignment structure 100as described previously in connection with FIG. 1, for example.

As also discussed previously, the fiber f is installed in the U-shapedport 152, which is part of the optical component interface 112 of themounting and alignment structure 100.

FIG. 20 is a process diagram illustrating the active alignment processthat is used in conjunction with the deformable optical componentmounting structures in the manufacture of an optical signal source asillustrated in FIG. 19, for example.

Specifically, in step 650, a laser die 614 and alignment structure 100are mounted to the optical bench 10 in a pick-and-place and bondingprocess. Specifically, a pick-and-place robot locates the die 614 andthe alignment structure 100 on the optical bench 10 using passivealignment. The alignment process is preferably accomplished usingmachine vision techniques and/or alignment features in the laser bench10, and mounting and alignment structure 100, and die 614, or explicitlyrelative to a defined coordinate system of the bench 10/module 622.

In step 652, once the laser hybrid 614 and structure 100 are attached tothe bench 10, wire bonding is performed to the laser hybrid. Then, instep 654, the laser 612 is electrically energized to determine whetheror not the laser is functioning properly.

If the laser is not functioning, then the optical system is rejected instep 656.

If, however, the laser is determined to be operational in step 654, thebench is moved to an alignment fixture of the production system in step658.

In step 660, the fiber f is inserted into the U-shaped port 152 of theoptical component interface 112 and bonded there. In the preferredembodiment, the fiber is solder bonded to bonding surface 132.

In step 664, the alignment system grasps or engages the mounting andalignment structure 100 to deform the mounting and alignment structure100 in response to a strength or magnitude of a signal transmitted bythe fiber f from the laser 612.

FIG. 21 illustrates the engagement between the alignment system and themounting and alignment structure 100 to align the fiber f. Specifically,the two jaws 710A, 710B engage the handles 136 of the mounting andalignment structure 100 and then move the mounting and alignmentstructure to displace the fiber f in an x-y plane, which is orthogonalto the axis of the fiber f. Simultaneously, the magnitude of the signaltransmitted by the fiber is monitored until a maximum signal is detectedin step 666 of FIG. 20. Of note is the fact that the right and leftcut-outs of the handle 136 enable the jaws of alignment system to bothpull and push the structure away and toward the bench 10, as needed toachieve an optimal alignment.

Returning to FIG. 20, once the maximum signal is detected in step 666,the alignment system further deforms the mounting and alignmentstructure 100 such that when the mounting and alignment structure isreleased, it will elastically snap-back to the desired alignmentposition detected in step 666. In other words, the mounting andalignment structure is plastically deformed such that it will haveproper alignment when the jaws 710A, 710B of the alignment systemdisengage from the mounting and alignment structure 100.

If it is subsequently determined in step 670 that the optical component,i.e., the fiber is not at the position associated with the maximumcoupling, the deformation step 668 is performed again until the positionis within an acceptable tolerance.

FIG. 22 is a plot illustrating the alignment process. Specifically, thefigure of merit or the coupling efficiency of light into the opticalfiber is plotted as a function of displacement of the optical fiber.Specifically, the coupling efficiency is maximized when the fiber islocated at the best alignment position and falls off on either side ofthis position.

FIG. 22 also illustrates force or stress as a function of strain ordisplacement during the several steps of the alignment process.Specifically, in a first step 710, force is exerted on the mounting andalignment structure, such that it undergoes elastic deformation. In thisregime, there is a substantially linear relationship between the appliedforce, on the y-axis and the displacement or strain on the x-axis. Oncethe yield force level is exceeded, however, the mounting and alignmentstructure 100 undergoes plastic deformation as illustrated by line 720.This plastic deformation results in permanent deformation to themounting and alignment structure.

When force is removed, the mounting and alignment structure undergoeselastic “snap-back” as illustrated by step 722. That is, with the forceremoved, the structure undergoes some elastic movement. However, becausethe yield force level was exceeded, the mounting and alignment structurehas been permanently deformed as indicated by distance Δ₁.

Even with this plastic deformation, the fiber is still not at the bestalignment position. As a result, another cycle of plastic deformation isperformed. Specifically, force is applied such that the mountingalignment structure undergoes elastic deformation as illustrated by line724. Once the new yield force level has been exceeded a second time, itthen undergoes plastic deformation as indicated by line 726. The yieldforce has increased during this second alignment cycle due to workhardening. Force is then removed and the mounting and alignmentstructure undergoes elastic snap-back as illustrated by line 728.

This second plastic deformation step, since it exceeded the yield force,resulted in movement toward the best alignment position of Δ₂.

Nonetheless, if optimal alignment is to be achieved, more plasticdeformation must be performed. Specifically, again the elasticdeformation is performed in step 730 until the yield force is reached.Then, a small amount of plastic deformation is performed as indicated byline 732. Force is removed and the mounting alignment structure nowsnaps back to the best alignment position as indicated by line 734.

The graph insert shows the figure of merit during the alignment process.During the first plastic deformation cycle, the position passes throughthe best alignment position, but after force is removed, the elasticsnap-back pulls it out of best alignment. During the second deformationcycle, the best alignment position is again passed and exceeded. Thissecond cycle, however, improves the alignment once force is removed.Finally, the third cycle brings the fiber into the best alignmentposition.

Mounting Structure Design Criteria

FIG. 23 presents a plot of force, F_(Y), as a function of displacementthat can be employed in accordance with the invention to design thearmatures for a given application. The yield force is the force at whichthe structure begins to undergo plastic deformation from an elasticdeformation regime.

The lower bound on F_(Y) (1200) is constrained by environmental shock,i.e., acceleration, and by the possible forces to which the mountingstructure might be subjected during handling. Some specificationsrequire optical systems to withstand 5000 g shock-tests. Typically withsome optical elements, yield forces of greater than 0.5 Newtons aretypically required. This number, however, can be reduced as the size andthus mass of optical elements is reduced. Were there no minimum yieldforce constraint, the unavoidable forces produced during handling,including fabrication, heat treatment, plating, pick and place,alignment, packaging, and other processes, could cause plasticdeformations of the flexure joints. More seriously, any shock to analigned system might misalign it, defeating one of the purposes of theinvention.

The upper bound on F_(Y) (1250) is constrained by three factors. First,the force required to cause plastic deformation of an armature orflexure must not be so high as to weaken or destroy the bond between themounting structure and the substrate. Second, the yield force must notbe so high as to cause significant elastic deformation in themicromanipulator that is applying the force. Third, the force requiredto deform the armature or flexure must not be so high as to damage otherportions of the integrally-formed mounting structure.

In addition to constraining the armature yield force, it is alsopreferred to constrain how much displacement is required in order toreach the yield point. The lower bound (line 1300) is dictated first bythe physical range of the structure. A mounting structure only functionsas desired if there is enough plastic deformation range to reach thealigned position. Generally, the alignment structures need to enablemovement or placement of the optical component of 0 to 50 microns. Thetypically alignment algorithms require plastic deformation that yields 4to 5 microns of movement in the position of the optical component toreach alignment. The second constraint on the minimum stiffness isdetermined by the amount of “overshoot” deemed acceptable by thealignment algorithm. If the structures are too elastic, then they mustbe pressed a long distance beyond the desired alignment point in orderto make even a small alignment adjustment.

The final constraint is the maximum stiffness of the flexures (line1350). Were work hardening not an issue, there would be no constraint onmaximum stiffness (except, of course, material limitations). With nickeland nickel alloys, however, work hardening occurs. Therefore, thestiffness upper bound is selected so that line 1250 is not exceeded evenwith work hardened created by successive plastic deformation cyclesperformed during the search for the correct alignment.

In the preferred embodiment, F_(Y, y), i.e., the yield force in thedirection of the y-axis, is less than 3 Newtons (N), typically between0.2 and 1 N. The yield force along the x-axis, F_(y, x) is similarlylimited to less than about 3 Newtons, typically between 0.2 and 1 N.Yield forces below 0.2 N are viable if smaller optical component areused, however. These lower limits are related to the mass of the opticalcomponent that the structure must restrain without unintended plasticdeformation. Thus, lower yield forces are possible with smallercomponents in subsequent product generations.

In contrast, the yield force the z-axis direction, i.e., F_(Y, z) orF_(Y, θ), is much larger to promote alignment in only the x-y plane.Preferably, F_(y, z) or F_(y, θ) are greater than 5 N or 10 N. Further,especially in versions of the alignment structures that are used tosecure fiber pigtails to benches. Thermal expansion mismatches resultingstresses on the fibers. The objective is to design the structures sothat such stresses result in as little movement in the fiber endface aspossible. Especially any rocking motion is desirably avoided bybalancing the structures by selecting the location of where thearmatures attach to the fiber component interface.

Further Embodiments

FIG. 24 illustrates another embodiment of the invention in which thestructure 100 is a composite of an extrusion-like portion 101, which hasa constant cross section along the z-axis, and two z-axis flexure pieces102, which control rotation around the x-axis or in the direction ofangle Θ_(x), thereby determining the resistance to force componentsalong the z-axis. Preferably on the z-axis flexure pieces 101 areseparately fabricated and bonded to base surface of portion 101. Basesurfaces of the pieces are then bonded to the bench.

FIG. 25 is an example mounting structure provided by the inventionwherein two different materials (indicated as “A” and “B”) are employedin the mounting structure for minimizing any change in optical axislocation due to thermal expansion and/or contraction of the structure.In one example configuration, the “A” material is selected, incombination with the design of that region of the structure, to expandupward due to temperature change, while the “B” material and itscorresponding mounting design features are selected for a tendency toexpand downward due to temperature change. These opposing expansiontendencies result in a compensating action that produces stability instructure geometry and position across a range of operationaltemperatures.

Optical System Production Line

FIG. 26 schematically illustrates the manufacturing sequence for opticalsystems according to the principles of the present invention. Generally,process comprises precision pick and place to locate the opticalcomponent to an accuracy of better than 10 microns, better than twomicrons in the preferred embodiment, followed by active alignment inwhich the position of the component is trimmed to an accuracy of about amicron, preferably better than a micron.

Specifically, an alignment structure supply 2010, such as a gel pack orother machine-vision compatible holder, is provided along with asimilarly configured optical component supply 2012.

Each of the supplies is accessed by a pick-and-place machine 2014.Specifically, the pick-and-place machine applies the optical componentsto the alignment structures and bonds the components. Typically, eitherthe alignment structures and/or the optical components are solder coatedor solder performs are used. The pick-and-place machine heats thealignment structure and the optical components and brings the two piecesinto contact with each other and then melts and resolidifies the solder.

In the current embodiment, the pick-and-place machine is manufactured byKarl Süss, France, type FC-150 or FC-250. These pick-and-place machineshave a vacuum chuck for picking-up the optical components and a holderfor holding the alignment structures.

The alignment structures, with the affixed optical components are thenfed to a separate or the same pick-and-place machine, which has accessto an optical bench supply 2018. In this second pick-and-placeoperation, the pick-and-place machine 2016 holds the optical bench on avacuum chuck or holder and then applies the alignment structure, withthe optical component, to the optical bench using its vacuum chuck. Thebench and structure are then heated to effect the solder bonding.Further, by matching alignment features of the benches and alignmentfeatures of the mounting structures, placement accuracies of less than 5microns are attainable. In the preferred embodiment, the structures arelocated on the bench with accuracies of better than 2-3 microns in aproduction environment.

In the preferred embodiment, the optical benches, with the alignmentstructures affixed thereto are then fed to an alignment system. Thisalignment system 2020 has the jaws 710A, 710B which grasp the handle ofthe alignment structure 100 to effect alignment. In the preferredembodiment, this alignment is active alignment in which the magnitude ofthe optical signal 2022 is detected by a detector 2024. The alignmentstructure 100 is manipulated and deformed until the optical signal 2022,detected by the detector 2024, is maximized. Alignment search strategiessuch are a hill-climbing approach or spiral scan approach are preferablyutilized.

In other situations, such as when installing optical fibers on the bench10, the alignment structure is preferably installed first without thefiber attached by the pick and place machine 2016. Then at the alignmentsystem, the fiber is fed through a fiber feed-through in the module andattached, such as by solder bonding, to the alignment structure 100.Then the alignment system manipulates the structure to effect alignment.

Once aligned, the optical bench and module is then passed to a lidsealing operation 2026 where the final manufacturing steps are performedsuch as lid sealing and baking, if required.

FIGS. 27A, 27B, and 27C illustrate three different configurations forthe alignment channels 118 introduced in FIG. 1.

FIG. 27A is the simplest design, but has a drawback associated withimplementation in machine vision applications when the base surface ispre-coated with solder, or other bonding agent. Solder fills in thecreases and smoothens the channel's edges making alignment based on thefeatures potentially less accurate.

FIGS. 27B and 27C show channels incorporating cavities in the featuresthat facilitate the identification of edges 118A even after soldercoating. The resulting clear edge features, even after coating,facilitate alignment during bench installation.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. An optical system active alignment processcomprising: attaching an alignment structure to an optical bench;measuring an optical signal after interaction with an optical componentheld on the alignment structure; an alignment system engaging anddeforming the alignment structure in response to the optical signal tofind a desired position for the optical component; and after the desiredposition is found, the alignment system engaging and plasticallydeforming the alignment structure so that the optical component of thealignment structure will be at the desired position when the alignmentsystem disengages from the alignment structure.
 2. A process as claimedin claim 1, wherein the step of engaging and deforming the alignmentstructure comprises applying force to the structure to elasticallyand/or plastically deform the alignment structure while detecting amagnitude of the optical signal.
 3. A process as claimed in claim 1,wherein the step of engaging and deforming the alignment structurecomprises engaging the alignment structure at a handle thereof.
 4. Aprocess as claimed in claim 1, wherein the step of engaging andplastically deforming the alignment structure comprises deforming thealignment structure beyond the desired position for the opticalcomponent to account of elastic movement of the alignment structureafter disengagement from the structure by the alignment system.
 5. Aprocess as claimed in claim 1, wherein the step of engaging andplastically deforming the alignment structure to locate the opticalcomponent at the desired position comprises moving the optical componentin a plane that is orthogonal to a propagation direction of the opticalsignal at the optical component while maintaining a position of theoptical component along an axis that is parallel to the propagationdirection of the optical signal.